Prevent a layer shell infinite looping case

[stacyharper]

This commit try to fix a case we encounter when running wayout, a layer
shell to display text above the background.

When running wayout, other layer shell start to consume 100% of the CPU.
This seems related to a previous fix 744e85b. Then later, another commit
reworks this handle_surface_commit method 5fd5d64.

https://todo.sr.ht/~mil/sxmo-tickets/413

This is a tentative to fix the issue without missing the points of those
patches.

We basically try to not re-arrange layers if no layer changed.

Related to : #6546

This patch seems to solve our issue, but am I missing something ?

[emersion]

cc @vyivel

The change looks fine to me, it seems like an oversight in the patches referenced above?

[vyivel]

I think this will break cases when a layer surface changes its keyboard interactivity but not anything else.

[emersion]

Shouldn't this be handled by layer_surface->current.committed != 0?

[vyivel]

With this patch, arrange_layers() will only be called if the layer has changed (which implies committed != 0).
At least for me, GitHub screws up indentation up making the flow of logic a bit hard to see; I recommend opening the full file.

[stacyharper]

This seems to cause some issues :

• Sometime the swaybar do not display itself. Had to open my virtual keyboard to make all layer shell to pop
• bemenu --center is not centered

[vyivel]

Right, because changing anchor is also not handled.

[vyivel]

Presumably what happens here is a loop of "Sway configures a layer surface <-> the client needlessly sets the same size/anchor/etc". While a client shouldn't really do this, it's perfectly valid behavior, so the fix would to be check not only committed mask but also if the values have actually changed.

[emersion]

wlroots could have this logic, so that compositors don't need to manually check this.

[vyivel]

That would make sense; also e.g. wlr_output_enable() unsets the flag if the value didn't change.
And for Consistency™ we would need to have the same logic everywhere. :P

[stacyharper]

I tried this : https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3402

It seems to work. What do you guys think of that ?

[emersion]

Superseded by the wlroots MR.